Self-injuries may have biochemical base: study

3/20/1998 - The same drive to feel good that pushes an addict's need for drugs may be behind one of the more puzzling and disturbing of behavior problems  self-injury by people with autism, mental retardation or other developmental disabilities.

Vanderbilt researchers have discovered strong evidence that people with autism or mental retardation who compulsively strike their heads or bite themselves may do so because it prompts biochemical changes in their brains.

In particular, certain forms of self-injury may prompt the release of a biochemical called beta-endorphin, the body's natural opiate. Beta-endorphin binds to the same receptors in the brain as heroin and morphine.

"While we can't say these patients feel a rush in the same way a heroin addict feels a rush, it may be a little like that," said Travis I. Thompson, Ph.D., director of the John F. Kennedy Center and professor of Psychiatry and Psychology.

"They may learn that they feel better when they do this."

As many as one in five people with mental retardation and more than half of people with autism injure themselves persistently, Thompson said.

The behavior typically begins at about the age when normal language should develop. It is believed that when language skills do not develop, the person begins to hurt himself, initially out of frustration at not getting his needs or wants met.

"They learn inadvertently that if they want Mom to do something and they bang their head against the floor, Mom tries to figure out what's wrong," Thompson said. "The problem gets fixed, even though it's a difficult way to solve a problem."

Thompson, who has been doing research in this area for about 15 years, said he first suspected a biochemical mechanism when observed a man with mental retardation become very agitated and anxious, then begin beating himself over the head.

"He would be all bloody and bruised from doing this, but immediately after he did it, he was calm," Thompson recalled.

Thompson said it reminded him of the behavior of heroin-addicted monkeys he had used in substance abuse research earlier in his career.

Making the connection that beta-endorphin is released when a person is injured, he and his colleagues decided to determine whether blocking the brain's opiate receptors would have an effect on self-injurious behavior.

"But we noticed that not everyone responded to the drug, naltrexone," he said. "About 30-50 percent showed pretty favorable responses but others didn't."

So he and Frank J. Symons, a former Vanderbilt graduate student who is now a researcher at the University of North Carolina, mulled over this problem. They remembered a paper by an undergraduate honors student involving group home residents that suggested people tend to injure themselves in common acupuncture sites.

While interesting, the paper did not use methods to ensure the reliability of the data, so Thompson and Symons developed a study that would test the notion.

The researchers collaborated with teachers in Metro schools on a study involving about 40 self-injuring students with a variety of developmental disabilities. More than half of them were autistic.

Using meticulous grids of the human body, the teachers and their aides carefully darkened squares representing where the students injured themselves. To ensure reliability, the researchers observed about 20 percent of the students and made their own recordings.

"Low and behold, 80 percent of the self-injuries occurred on about 5 percent of the body surface, and that 5 percent corresponded to common Chinese acupuncture sites," Thompson said.

Their findings, reported in the December 1997 issue of the Journal of Intellectual Disability Research, lend further support to the idea that beta-endorphin is involved in certain forms of self-injury. According to established medical literature, levels of beta-endorphins in the bloodstream rise  as does the tolerance for pain  when acupuncture sites are electrically stimulated, Thompson said.

Acupuncture itself is not likely to be a practical treatment because the effects would be too transient, he said, but the finding is helping target the most effective treatment more quickly.

"We can now predict pretty well which people are going to respond to naltrexone by where they injure themselves," he said. "We combine that with communication training because without alternatives to get their needs met, they'll relapse just an addict would. If the world is no longer working for them, they'll go right back to what used to work, which was banging their heads on the table or biting the back of their hands."

Thompson cites the experience of one boy who was identified as a potential responder to naltrexone. He was treated with naltrexone and communication training.

"Now, two years later, his teachers don't know he self-injured, and he's no longer considered a behavior problem," Thompson said.

"That's typical of what we see. The results are very gradual, come on very slowly, but if you stick with it over a couple of months, the problem will usually go away.

"It's an interesting phenomenon. It looks to us as though these patients probably accidentally discover sites that make them feel better and begin to focus on those sites as they get older."

Thompson said he suspects different biochemical mechanisms underlie different types and intensities of self-injury, and that in some patients, a combination may be involved.

For instance, patients with a rare genetic disorder called Prader-Willi Syndrome often engage in persistent and compulsive skin picking, Thompson said. This behavior does not respond to naltrexone but it often does respond to SSRI antidepressants.

Thompson said he is interested in collaborating in the future with Dr. Merlin G. Butler, associate professor of Pediatrics and Pathology, and Dr. Randy D. Blakely, Allan D. Bass Chair and associate professor of Pharmacology, to learn more about how the serotonin pathway may be linked to self-injury. Butler and Blakely currently are working to identify genetic subtypes among autistic patients involving the serotonin transporter gene.

"We need to be able to do a better job of diagnosing the nature of the condition so we can prescribe a more effective treatment much more expeditiously," Thompson said.

"It would be so much better if we knew right up front what the person needs and start with that right away."